Since then, numerous studies investigating miRNA expression levels in RA have been performed, mainly in synovial joint tissue (14, 15) but also in serum (16), peripheral blood (16, 17), peripheral blood mononuclear cells (PBMC) (15, 17), blood-derived CD4+ T cells (15, 18) and specific CD4+ T cell subsets (19). Here, CD4 is linked to rheumatoid arthritis.